Avoid Serialization and Deserialization

Serialization and deserialization of objects is a CPU-intensive procedure and
is likely to slow down your application. Use the transient keyword
to reduce the amount of data serialized. Additionally, customized readObject() and writeObject() methods may be beneficial in some
cases.

Use StringBuffer to Concatenate Strings

To improve performance, instead of using string concatenation, use StringBuffer.append().

String objects are immutable—they never change after creation. For example,
consider the following code:

Therefore, copying is inherently expensive and overusing it can reduce performance
significantly.

Assign null to Variables That Are No Longer Needed

Explicitly assigning
a null value to variables that are no longer needed helps the garbage collector to
identify the parts of memory that can be safely reclaimed. Although Java provides
memory management, it does not prevent memory leaks or using excessive amounts of
memory.

An application may induce memory leaks by not releasing object references. Doing
so prevents the Java garbage collector from reclaiming those objects, and results
in increasing amounts of memory being used. Explicitly nullifying references to variables
after their use allows the garbage collector to reclaim memory.

One way to detect memory leaks is to employ profiling tools and take memory
snapshots after each transaction. A leak-free application in steady state will show
a steady active heap memory after garbage collections.

Declare Methods as final Only If Necessary

Modern optimizing dynamic
compilers can perform inlining and other inter-procedural optimizations, even if Java
methods are not declared final. Use the keyword final as it was originally intended: for program architecture reasons and maintainability.

Only if you are absolutely certain that a method must not be overridden, use
the final keyword.

Declare Constants as static final

The dynamic compiler can perform some constant folding optimizations easily,
when you declare constants as static final variables.

Avoid Finalizers

Adding finalizers
to code makes the garbage collector more expensive and unpredictable. The virtual
machine does not guarantee the time at which finalizers are run. Finalizers may not
always be executed, before the program exits. Releasing critical resources in finalize() methods may lead to unpredictable application behavior.

Declare Method Arguments final

Declare method arguments final if they are not modified in
the method. In general, declare all variables final if they are
not modified after being initialized or set to some value.

Synchronize Only When Necessary

Do not synchronize code blocks or methods unless synchronization is required.
Keep synchronized blocks or methods as short as possible to avoid scalability bottlenecks.
Use the Java Collections Framework for unsynchronized data structures instead of more
expensive alternatives such asjava.util.HashTable.

Use DataHandlers for SOAP Attachments

Using a javax.activation.DataHandler for a SOAP attachment
will improve performance.

JAX-RPC specifies:

A mapping of certain MIME types to Java types.

Any MIME type is mappable to a javax.activation.DataHandler .

As a result, send an attachment (.gif or XML document) as
a SOAP attachment to an RPC style web service by utilizing the Java type mappings.
When passing in any of the mandated Java type mappings (appropriate for the attachment’s
MIME type) as an argument for the web service, the JAX-RPC runtime handles these as
SOAP attachments.

For example, to send out an image/gif attachment, use java.awt.Image, or create a DataHandler wrapper over your image. The advantages
of using the wrapper are:

Reduced coding: You can reuse generic attachment code to handle the
attachments because the DataHandler determines the content type of the contained data
automatically. This feature is especially useful when using a document style service.
Since the content is known at runtime, there is no need to make calls to attachment.setContent(stringContent, "image/gif"), for example.

Improved Performance: Informal tests have shown that using DataHandler
wrappers doubles throughput for image/gif MIME types, and multiplies
throughput by approximately 1.5 for text/xml or java.awt.Image for image/* types.